Engines may utilize variable cam operation to adjust intake and exhaust valve operation in an engine cylinder. For example, the cam timing may be adjusted to improve engine operation across a range of conditions. In one example, a control system maintains the cam timing relative to crankshaft timing based on feedback information from cam and crankshaft sensors.
U.S. Pat. No. 6,932,033 describes one approach to control cam timing based on a toothed cam wheel with an additional index tooth. The index tooth indicates when a torque reversal occurs on the camshaft. The control system adjusts the cam actuator based on this information to provide improved cam timing control. Additionally, the uneven tooth can provide identification information used during engine starting to identify engine position, as the crankshaft does not uniquely identify engine position in a four-cycle engine.
The inventors herein have recognized some issues with the above approach. For example, while an increased number of evenly spaced teeth provide an increased data rate of sensed cam position, the single uneven tooth may lead to longer engine cranking. For example, up to two full crankshaft revolutions may occur before the uneven tooth is identified in order to identify engine position and commence sequential fuel injection. On the other hand, reducing the number of evenly spaced teeth in order to provide earlier engine position identification can lead to reduced data rates of sensed position during engine running.
The inventors herein have recognized that this apparent paradox can be at least partially addressed by incorporating information from uneven tooth edges into the feedback control of cam operation in one embodiment. For example, an engine method includes adjusting a variable cam actuator responsive to cam position feedback from even and uneven readings of a cam sensor.
In this way, it is possible to provide quick engine position identification during an engine start through a plurality of uneven tooth edges, while maintaining a high data rate of sensed cam position, and thus accurate control of cam operation, from both even and uneven tooth edges.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.